Production of metallurgical coke



U it d St te PRODUCTION OF METALLURGICAL COKE Clarence R. Lohrey, Ontario, Calif., assignor to Kaiser Steel Corporation, Oakland, Calif., a corporation of Nevada No Drawing. Application January 29, 1951, Serial No. 208,437

11 Claims. (Cl. 202-33) The present invention relates to a process and material for the production of high grade metallurgical coke. More particularly, the invention relates to a process for the production of a high grade metallurgical coke from high volatile coking coals by blending therewith relatively small amounts of a particular type of petroleum coke. .One of the most critical factors in the production of a satisfactory coke for use as a metallurgical fuel, for example in the reduction of iron ore in blast furnaces, is the structural stability or crushing strength of the product of the coke ovens. A high stability factor or compressive strength is essential in such a metallurgical coke in order that it Withstand the high compressive stresses exerted due to its own superimposed weight and the weight of the other raw materials in the furnace charge. Excessive production of fines due to crushing of the coke would lead to inefiicient blast furnace operation and excessive loss ofthe fuel in the form of flue dust.

1 High volatile coking coals, such as commonly found inj'the western coal deposits of the United States, although producing a coke satisfactory in regard to ultimate chemical analysis, result in a coke lacking in certain physical properties necessary in a good grade metallurgical coke. The principal deficiency in the cokes produced from such coals is the low stability factor or crushing strength which renders them unfit or unsatisfactory as a metallurgical fuel, for example for use for blast furnace operations.

Extensive development work has been conducted in the past to evolve processes or additives for such high volatile coking coals to modify the coke produced therefrom so that it would have a high crushing strength suflicient to meet the requirements for use as a metallurgical coke. For instance, various blends of lowvolatile coking coals and high volatile coals have been utilized to modify the physical properties of the coke produced from the high volatile coal alone. Metallurgical coke of satisfactorily high crushing strength has been. produced from certain blends of these materials.- However, .such low volatile coals unfortunately are not always readily available and often must be transported over such'distances to the blast furnaces or other metallurgical operations, that the cost of producing the, coke makes the use of the low vola- 1. tile coal uneconomical. Moreover, the reserves of low coke of suificient hardness factor or crushing strength to be. suitable for metallurgical uses, in particular blast furnace operations where the coke is subjected to severe conditions regarding structural stability. Accordingly,

the need for a petroleum coke having the proper characteristics so that when blended with a high volatile coking coal, the mixture would produce a desirable metallurgical grade coke, remained unsatisfied.

It is a primary purpose and object of the present invention to provide a process and a composition or material by which high grade metallurgical coke may be produced from high volatile coals. A more specific object is to provide a process and a composition essentially comprising high volatile coals and specified amounts of petroleum coke having certain specific characteristics by means of which a coke having a sufficiently high crushing strength for use as a metallurgical fuel is produced.

Another object or advantage of the invention is to provide a blend of high volatile coal and petroleum coke of certain specified characteristics, which when used as a raw material for the production of metallurgical grade coke can be subjected to the normal conditions employed in the coking ovens for ordinary good coking coals without requiring any substantial or significant change in operations or modifications of the apparatus conventionally employed. It is a further advantage of the invention that the production of high grade metallurgical coke from high volatile coals is accomplished by blending relatively small amounts of the particular petroleum coke with such coals. These and other objects and advantages of the invention will become apparent from the following detailed description thereof.

It has been discovered, according to the invention, that coke from high volatile coals particularly suitable for metallurgical fuel is produced by blending with the coal a petroleum coke having a volatile matter content different from that contained in petroleum coke produced under conventional conditions in those refinery operations giving rise to coke formation, such as distilling and cracking. In particular, it was found that a petroleum coke having a range of volatile matter from about 14 to about 24% by weight when mixed with high volatile coking coals and the mixture subjected to normal coking conditions in by-product coke ovens or other suitable apparatus produced a metallurgical grade coke of excellent crushing strength. In addition to the production of the improved coke in regard to the quality for the purpose intended, this blend of coal and coke increased the yield of fractions most desirable for metallurgical purposes,

that is, there was a minimum production of coke breeze (fines) and nut coke. The most satisfactory results are obtained when the volatile matter of the petroleum coke is within the range of 16 to 22%, and accordingly this range is preferred.

The invention does not embrace the particular refinery operations which lead to the production of petroleum coke having the above specified properties, but is directed primarily to a blend of such petroleum coke with high volatile coals and the process for production of a metallurgical grade coke therefrom. Accordingly, it is intended that the invention embrace petroleum coke of the above specified volatile material content regardless of the palticular manner in which such coke is obtained. However, in order to illustrate one method of producing such a petroleum coke reference is made to U. S. PatentNo. 1,919,157 issued to Virgil Lee Board, July 18, 1933. The so-called intermediate coke therein fully described exemplifies a petroleum coke suitable for the present invention. The pressurecracking method employed on the oil to produce this intermediate coke is fully set forth in the patent.

Petroleum coke having the above indicated volatile matter content is' blended with any high volatile weakly coking coal and the-mixture is-crushed to conventional particle size range-for-charging to the usual coking operat-ions. The most desirable results from-the-pointof view of economy and with regard to the properties of the metallurgical coke produced are observed when from about '7 -to 25% of petroleum coke by weight of the mixture is employed. Amounts of petroleum coke substantially below 5% do not appear to modify the structural stability characteristics of the coke product sutii ciently to make it entirely satisfactory for use as a metallurgical fuel, for example, 'for blast furnace operation. However, any minor amount of pW-rC-leum coize from about 3% up to slightly less than 50%.may be em ployed with entirely satisfactory results. Amounts sub stantially in excess-cf are less economical and are not necessary for requisite strength, but may be-utilized whcnthc cok'e is cheap and readily availnbic. When the blend consists entirely of petroleum coke and high VOiEh tile cool. the mixture therefore consists of from about 97% down to slightly more than by weight of the latter.

The invention also embraces the presence of certain other materials in the coke-coal blend in minor amounts, although the blend consisting of petroleum'coke and coal representsthe presently preferred embodiment of the invention. Where it is readily available, low volatile coal may be added to the blend .as a substitute for a portion of the petroleum coke which would normally be used. For sample. a blend usually containing about 10% coke may instead contain 5% coke and 5% low volatile coal. stitutes a major proportion by weight of the blend, that is, over 50%. It is preferred, when substituting low volatile coal that the amount not exceed about one-half of the petroleum coke.

in addition, the blend may also contain a small amount of a relatively hard pitch having characteristics hereinafter mentioned, for example. lay-product pitch from the coal tar plant process in amounts up to about 5% by weight of the mixture. The :pitch is substituted for a small portion of the high volatile coal, for examplmin a blend of 75% high volatile coal-25% petroleum coke, the high volatile may be reduced to 76% with 5% pitch substituted. Thus, the pitch is substituted in equal amount for the high volatile coal.

In all cases, whether the coking mixture contains only high volatile coal and petroleum coke, or contains in addition minor amounts of low volatile coal and/or small amounts of pitch, the coke products resulting have properties distinctly superior to those resulting from the coking of similar compositions except that the petroleum coke constituent does not contain the specified range of volatile matter. This is particularly true with regard to the structural stability or crushing strength of the coke.

The blend of high volatile coal and petroleum coke with or without any of the above mentioned additional constituents, is charged to the coking apparatus, for example, a vertical by-product coke oven which is scaled against admission of air as in normal coking practice and is then subjected to coking temperature until coking action is completed producing the desired hard, dense metallurgical coke. The oven temperature depends upon length of coking time, width of oven, capacity of oven and other factors. For a given rate of operation of the oven, the wall of the oven may have a temperature of about 2100 F. and a heating flue temperature of about 2300 vF. However, the effective temperature of coking will vary widely depending-upon the :rate of operation audis adjusted to a given rate as in ordinary coking operations to produce a high grade metallurgical coke, high in fixed carbon, low in volatile and ash and with a sulfur content a iaptcd to the intended purpose. The resulting coke is a product fundamentally distinct from the petroleum coke and high volatile coal and any other ingredients of the raw material mixture in that it is higher in fixed carbon, much lower in volatiles and much harder and firmer in However, in all cases the high volatile coal con- 4 structure with an excellent crushing strength or structure stability.

The coke may be discharged from the ovens without diiiiculty after the oven vents are opened and is pushed into a quenching car or other receptacle where it is quenched, preferably with water, in accordance with ordinary'cokingmractice.

The coke is discharged from the ovens in a hard solid state and of good size with a hardness factor ranging fromabou't to over'TO by'the A. S. T. M. tumbler'tcst and is adapted to carry a heavy burden which makes it particularly suitable for -.use.in blast furnace operations.

The invention is furtherillus'trated :in detail with reference to the following examples in the table below setting forth the results of a'nurn'ber of experimental runs which were made in accordance with the present invention. These tests were made using so-called lower Sunnyside coals, which are Utah coals classified as high volatile B: bituminous and having the proximate analyses indicated in the table below. The samples were cokcd in a byproduct oven at a tempera'ture of from 2030 to 2130 F. for 18 hours, and then quenched and dried.

'Thecoke produc'tswere then'subjected to the A. S. T. M. tumbler 'tcst for-determination of stability and hardness factors, and tie the -A. 'S. T. M. drop shatter test for determination-of property of the coke to withstand breakage during handling and in transit. For details concerning such tests reference may be made to A. S. T. M. Standards, Pa1't 5, l949,pages 672 to 674, and pages 675 and 676, respectively, published by the American Society for Testing Materials.

in the tumblcr'test, which provides a relative measure of resistance of the coke to degradation by abrasion and to a certain extent influenced by the effect of impact, samples .ofa size range 'of from 2 to 3 inches are weighed and then'tumbled in a'drumrotating at about 25 R. P. M. forl4010 revolutions. lhecoke is then sieved successively onscreens of .2, 1.5, 1.06, 0.530, and 0.265 inch mesh and each fractionseparately weighed. The stability factor is the pcrceutof cokeretained on the 1.06 inch sieve and the hardness factor is the percent retained on the 0.265 inch sieve.

In regard .to the drop .shatter test, the table gives only the percent coke retained on the 2 .inchscrecn.

The itablei-also gives the percent of plus .Zinch material in the coke determined by. sieve analysis on the oven products. 'In addition, the physical fuelyalueandproximate analyses of the cokes from each sample are given.

Coal-petroleum coke mixture By Weight Proximate Analysis @est No. Tercen't Percent 1310, .Ash, SuL, V. M., F. 0., Pet. .11. V. Per- Pcr- Per- Percent Percent Coke Goal cent cent cent 1 .-.d. .100 37. 2 10 8. 0". D0 38. 3 i 3 97 Coke 1 Physical Properties Proxlmate Analysis ASTM Physical Test No. ASTM Tumbler ASTM AS'IM Fuel +2 +2" Value V. MA Ash Sul. F. 0. Shatter Screen Stability Hardness 1 V. M.=volati1e matter.

From the foregoing'data, it may be seen that the coke from 100% high volatile coal is relatively deficient in stability factor, that is, easily degraded by abrasion and crushing. Thus, the stability factor of the cokes of the present invention is at least 50% higher (compare tests 1 and 6) within the preferred range of amounts and even as low as 5% petroleum coke, and in some cases increases to almost four times higher than the coke from 100% high volatile coal (see test 12). In addition, the fuel values of the cokes of the present invention are significantly higher, that is, from about 50% up to as much as about 2 /2 times higher, while the resistance to breakage by impact is at least more than doubled.

With respect to coke produced from the petroleum coke of so-called normal volatile content, for example, the coke of test number 2 containing only 8.5% volatile matter, blended with high volatile coal, the hardness factor is deficient, that is, too large an amount is degraded by abrasion and crushing to sizes under 0.265 inch and the coke product is therefore too high in coke breeze or fines for a truly suitable metallurgical fuel.

The coke of the present invention produced from the particular blend of petroleum coke of specified volatile matter and high volatile coal has excellent stability and hardness factors, is of high fuel value, and of good size, and resists breakage due to impact. The crushing strength or stability and hardness values are at least comparable to values obtained in cokes produced from coals, which when coked alone produce excellent metallurgical fuel. Until the present invention no satisfactory metallurgical cokes of sufliciently high crushing strength and hardness factor had been produced from blends of petroleum coke and high volatile coals, and the hardness fiactor of the products of the present invention is appreciably increased over any previously prepared cokes of this general character, that is, containing petroleum coke and high volatile coal in the raw material charge.

It is to beunderstood that although precise proportions of the constituents of the raw material composition and exact conditions for coking have been set forth above in connection with the exemplary data, the invention is not limited to these precise proportions or to the particular manner of preparation of the petroleum coke or the ultimate product, that is, the metallurgical coke.

It is to be understood that the present invention in regard to the process for the production of the high grade metallurgical coke may utilize temperatures ranging from about l600 to about 2700 F. and the coking time may be varied from about 14 to about 72 hours depending upon the rate of operation of the coking ovens and the temperature employed. These factors such as temperature and reaction time depend upon the size of the retort and oven used, the quantity of the charge and similar factors which may be varied as desired.

It is only critical, that the petroleum coke have the volatile matter content specifiedand that it be used in amounts with the high volatile coal and other constitu ents approximating the ranges set forth. Accordingly, the scope of the invention is commensurate with the following claims Which recite the essential elements of the composition and the process necessary for the production of high grade metallurgical cokes of high crushing strength from high volatile coals.

What is claimed is:

l. A composition for the production of metallurgical coke consisting essentially of from about 75 to about 93% high volatile weakly coking coal and about 7 to about 25% by weight petroleum coke having a volatile matter content of from about 14 to about 24% by weight.

2. A composition according to claim 1 in which pitch from coal tar distillation is substituted for a portion of the high volatile coal in etn'ective amounts up to about 5% by weight of the mixture.

3. A composition according to claim 1 in which low volatile coal is substituted for petroleum coke in'amount not exceeding about one-half of the latter.

4. A composition according to claim 1 in which hard tar pitch is substituted for the high volatile coal in amounts up to about 5% by weight of the mixture, and low volatile coal is substituted for a minor portion of the petroleum coke.

5. A method for the production of a metallurgical grade coke from high volatile weakly coking coals which yield a coke of ins'ufiicient crushing strength for metallurgical purposes, comprising mixing with a major amount of the high volatile coal from about 7 to about 25% by weight petroleum coke having a volatile matter content of from about 14 to about 24% by weighhand subjecting the mixture to coking temperatures until coking action is completed producing a metallurgical coke having a crushing strength superior to that produced by coking only the high volatile coal.

6. A method according to claim 5 in which the coal is present in amounts from about 75 to about 93% by weight.

7. A method according to claim 5 in which pitch from coal tar distillation is substituted for a portion of the coal in amounts up to about 5% by weight of the mixture.

8. A method according to claim 5 in which low vol atile coal is substituted for a minor portion of the pctroleum coke in the mixture.

9. A method according to claim 5 in which coal tar distillation pitch is substituted for high volatile coal in amount up to about 5% by weight of the mixture, and low volatile coal is substituted for a portion of the petroleum coke in amount not exceeding one-half of the latter.

10. A method of producing a high grade metallurgical coke from high volatile bituminous coals of the Utah type comprising mixing with from about 75 to 93% by weight high volatile coal, about 7 to 25% of a petroleum coke having from about 16 to 22% volatile matter, and

7 subjecting the mixture to coking temperatures of from about 1600 to about 2700 F. in 1a hy=pnoduct.coke.oven to produce a coke having a crushing strength, as-indicated by the ASTM stability factor, at least.50% higher than that of the coke produced from coking the high volatile coal alone.

11. A composition for the production of metallurgical coke consisting essentially of fromabout 75 to about 93% high volatile Weakly coking coal :and about 7 to about 25% petroleum coke having a volatile matter content of from about 16 to about 22% by weight, and up to about 5% of pitch from coal tar distillation substituted for a corresponding amount of fh'igh volatile coal, all by weight of the mixture.

References Cited in the 551:. of this patent UNITED STATES PATENTS 1,182,738 Becker May 9, 1916 1,407,700 Markle Feb. 28, 1922 1,796,465 Komarek. a... -23.. Mar. 17, 1931 August 1943, pages4,r5, 11,112, 13, 15, 16a11d 17.

1,815,918 Knowles July 28, 1931 1,824,526 Andrews Sept. .22, .1931 1,890,349 Weiss Dec. 6, 1932 1,919,157 Board -July 18, 1933 5 1,941,472 tBun'ce 2------ Jan. 2, 1934 2,158,816 Curran May 16, 1939 2,177,226 Rice Oct. 24, 1939 2,382,809 Otto Aug. 14, 1945 2,600,078 -Schutte -et a1. June 10, 1952 10 2,640,016 Martin May 26, 1953 FOREIGN PATENTS 341,877 Great Britain Jan. 12, 1931 OTHER REFERENCES 3 Society of' chemicalIndustryJournaLvol. 51, No. 22;

pp. 467469,'May 27, 1932.

Industrial and-Engineering Chemistry, vol. 36, No. 12, pp. 1140-1144, December 1944. 20 Bureau of Mines Report of InvestiI'gation, RI 3717, 

1. A COMPOSITION FOR THE PRODUCTION OF METALLURGICAL COKE CONSISTING ESSENTIALLY OF FROM ABOUT 75 TO ABOUT 93% HIGH VOLATILE WEAKLY COKING COAL AND ABOUT 7 TO ABOUT 25% BY WEIGHT PETROLEUM COKE HAVING A VOLATILE MATTER CONTENT OF FROM ABOUT 14 TO ABOUT 24% BY WEIGHT. 